Mineral fibers are used in a variety of products. The fibers can be used as reinforcements in products such as plastic matrices, reinforced paper and tape, and woven products. During the fiber forming and collecting process numerous fibers are bundled together as a stand. Several strands can be gathered together to form a roving used to reinforce a plastic matrix to provide structural support to products such as molded plastic products. The strands can also be woven to form a fabric, or can be collected in a random pattern as a fabric. The individual strands are formed from a collection of glass fibers, or can be comprised of fibers of other materials such as other mineral materials or organic polymer materials. A protective coating, or size, is applied to the fibers which allows them to move past each other without breaking when the fibers are collected to form a single strand.
Typically, continuous fibers, such as glass fibers, are mechanically pulled from a feeder of molten glass. The feeder has a bottom plate, or bushing, which has anywhere from 200 to 10,000 orifices. In the forming process, the strand is wound around a rotating drum, or collet, to form, or build, a package. The completed package consists of a single long strand. It is preferable that the package be wound in a manner that enables the strand to be easily unwound, or paid out. It has been found that a winding pattern consisting of a series of helical courses laid on the collet builds a package that can easily be paid out. Such a helical pattern prevents adjacent loops or courses of strand from fusing together should the strand still be wet from the application of the size material. The helical courses are wound around the collet as the package begins to build. Successive courses are laid on the outer surface of the package, continually increasing the package diameter, until the winding is completed and the package is removed from the collet. A strand reciprocator guides the strand longitudinally back and forth across the outer surface of the package to lay each successive course.
FIGS. 1 and 2 show a conventional winder 5 with a strand supply 40. Fibers 43 are drawn from a plurality of orifices 42 in a bushing 41 and gathered into a strand 44 by a gathering member 45. Size is applied to coat the fibers by size applicator 46. The strand 44 is wound around a rotating collet 31 to build a cylindrical package 20.
The package, formed from a single, long strand, has a radially outer surface 21 with edge portions 22 and a central portion 23 between them. The edge portions 22 form generally right angles with the package ends. The outer surface 21 of the cylindrical package 20 is typically between about 10 cm and 40 cm long, but may be longer or shorter depending on the application. The collet 31 is rotated about an axis of rotation 33 by a motor 35. A package core 32, such as a cardboard tube is disposed on the collet to receive the strand package.
The winder 5 includes a strand reciprocator 10 that guides the strand 44 laterally back and forth across the package surface 21 to lay the strand in courses 24 on the package surface. The strand reciprocator 10 includes a cylindrical cam barrel 11 mounted for rotation and has a helical groove. A cam follower is disposed in the groove and extends outwardly from the cam. A strand guide 16 is attached to the end that extends from the cam and includes a notch formed in the strand guide 16 to hold the strand 44. Rotation of the cam causes the cam follower to follow the helical groove, thereby causing the strand guide to move laterally across the package surface, placing the strand on the package in a desired location.
The winding apparatus 30 operates as follows. The strand reciprocator 10 guides the strand 44 as it is laid on the outer surface of the package 20, which rotates in a winding direction 34. The strand 44 is held by a notch in the strand guide 16 and wound around the rotating collet 31 or a package core 32 disposed about the collet. The cam is oriented near the package and rotates about an axis generally parallel to the package axis of rotation 33. As the cam rotates, the cam follower is moved laterally by the helical groove in a direction generally parallel to the package axis of rotation 33. The helical groove is continuous, with curved ends that cause the cam follower to move to the end of the package and then reverse direction. The strand guide is attached to the cam follower and it traverses the outer surface of the package, reciprocating back and forth from end to end.
As the package builds, the outer radius increases. To accommodate the increasing package radius, the strand reciprocator 10 is mounted on an arm 12. As the package radius increases, the arm 12 moves away from the collet 31 along line 17 to maintain the desired spacing between the reciprocating mechanism and the outer surface of the package.
A schematic view of strand courses on the wound package is shown in FIG. 5. The strand courses are produced by the strand guide moving from right to left to the end of the package and then back to the right in the sequence indicated by the arrows in FIG. 5. For ease of illustration, the entire outer surface of the package is shown, as though the package were cut along a longitudinal line and laid flat, and is not drawn to scale or necessarily representative of an actual package geometry. As used herein, the term "course" is defined to mean the double helical strand path produced by winding the strand around the package while traversing the strand guide through a full traverse cycle. The traverse cycle is defined and illustrated herein as starting at the center of the package, moving to one end of the package, across the length of the package to the opposite end, and then returning to the center of the package. Thus, a first course 310 begins on centerline C of package 300 at point 311. First course 310 has segments 312, 313, 314, 315, 316, 317, and 318, with each segment representing one rotation of package 300. Segment 318 represents a partial rotation of package 300, and ends at point 319 on centerline C. The course segments along the central region 302 of the package 300 are straight segments, since the strand guide is moving laterally at a constant velocity and the package is rotating with an approximately constant tangential speed. The strand guide must slow down and change direction once it reaches the end portions 304, 306 of the package. The strand guide therefore produces a transition or turnaround strand segment at each end 304, 306 of the package (segments 313, 316). Each turnaround segment corresponds to the slowing down and turning around of the strand guide and includes an arcuate portion and adjacent straight portions. The linear velocity of the strand guide decreases along the arcuate portion to zero at a tangent point in the center of the arcuate portion (at the edge of package 300) and then increases until it reaches the steady state traverse speed at the beginning of the straight portion.
Half of a second course 320 (illustrated by broken lines) is also illustrated in FIG. 5. Course 320 begins at the end point 319 of the first course 310 and includes straight segment 321, turnaround segments 322 and 323, and straight segment 324. For ease of illustration, second course 320 is not shown on the right side of package centerline C.
It is important to accurately control the placement of the strand on the package in the desired location, and to maintain the strand in the position in which it is laid, to properly build the package. This is particularly important in the transition portions of the transition courses. One undesired artifact of insufficiently precise strand control is referred to as "stitching." Stitching occurs when a portion of the turnaround segment moves from its laid position and extends beyond the package edge. The "stitch," or loop of strand, is exposed to wear and breakage, compromising the integrity of the package and its usefulness to the end user. One of the approaches that has been used to control the placement of the strand on the package and to maintain the strand in the position in which it was placed is the roller bail.
A roller bail mechanism is disclosed in U.S. Pat. No. 5,756,149 to Smith and is illustrated in FIGS. 1 and 2. The strand reciprocator 10 includes a roller bail assembly 18 for holding the strand courses 24 in place at the edge portions 22 of the package surface 21 as the strand guide 16 changes direction. The roller bail assembly 18 includes a pair of spaced, or split, rollers 19. The rollers 19 have generally cylindrical edge ends and tapered inner ends. The cylindrical edge ends contact the package surface 21 at the edge portions 22. The tapered inner ends extend from the edge portions towards the central portion 23 of the package surface 21.
As the strand guide approaches the edge of the package 20, the strand 44 is laid on the package surface under the roller tapered inner edge of a split roller 19. The strand guide continues to move towards the edge of the package and the strand course moves between the package surface and the cylindrical edge end of the roller, which is in contact with the package surface. When the cam follower travels through the curved end of the groove, the strand guide 16 changes direction and moves away from the package edge and towards the central portion of the package 20. The contact between the roller bails and the package surface holds the strand course turnaround segment in place at the edge of the package surface 20, when the strand guide changes direction. The turnaround segment of the course tends not to move away from its position after more of the course is wound on to the package as sufficient friction is produced between the course and the package surface by the tension on the strand. Because the roller bail presses against the outer surface the package in the package's end regions, it slightly flattens the package surface in the end regions from the slightly arcuate shape it would otherwise take. The pressure of the roller bail also helps to secure to the package surface the turnaround segments of previously-laid strand courses. This further aids in retaining the turnaround segments in the positions in which they were placed.
The roller bail mechanism reduces, but does not eliminate stitching, and suffers from other drawbacks. The rollers rotate at high speeds, requiring precise bearings and careful lubrication. Since the rollers contact the surface of the package, any difference in tangential speeds of the package and rollers, or even excessive friction in the rollers' bearings, produces drag forces on the surface of the package, which can damage the strand. The rollers wear, and are expensive to replace. Another problem with the roller bail mechanism relates to strand free length.
Strand free length is defined as the distance between the point of contact of the strand on a strand guide structure and the point of contact of the strand with the package. In the winder shown in FIG. 2, the free length 47 is the portion of the strand 44 between the guide 16 and the contact point between the split rollers 19 and the package. Since the strand is very flexible, lateral forces applied to the strand by the guide eye do not directly control the position of the strand along the free length. Thus, rapid deceleration of the guide eye at the end of the cam stroke is not transmitted directly to the full free length of the strand, and the momentum of the free length can carry it beyond the intended end of the package, producing stitching. There is sufficient variability in the dynamics of this process that it cannot be fully compensated for in the control of the guide eye alone. Thus, it is desirable to reduce free length to the minimum possible value.
In another known strand reciprocator, the guide eye maintains contact with the surface of the package during winding to control the package shape. As shown in FIG. 3A, package 20 is rotated in a clockwise direction, pulling strand 44 downward through the strand guide 50. The strand guide 50 is mounted to a traversing mechanism (not shown) which reciprocally traverses the strand guide along the package. Strand guide 50 includes a package engaging portion 51 which engages the outer surface 21 of the package 20 during operation. The planar surfaces 52 of the package engaging portion 51 remain in continuous contact with the outer surface of the package as the strand guide 50 reciprocates. The strand guide 50 is mounted to a cam follower by way of a pivotal mount 55. As shown in FIG. 3B, strand 44 is engaged in slot 54 of the strand guide 50. Slot 54 is tapered so that its depth decreases from the upper end to the lower end.
Since the strand guide 50 continuously contacts and compresses the package, it can only be used when winding a package on which the strand is wound with relatively low tension and therefore which is not tightly compressed by the winding forces. The package can therefore be compressed by the strand guide at the ends (where the package would otherwise build to a larger diameter than the center, i.e. has a "dogbone" shape) to produce a cylindrical outer surface. Otherwise, the strand guide will damage the package.
Strand guide 50 also includes a "wing" portion 53, shown in FIGS. 3A-3D, which is used to guide a strand located laterally outside slot 54 into engagement with the slot 54. This feature is used at the initiation of winding a new package by guiding the strand into the region traversed by the strand guide, which will engage the strand on the wing portion and then urge it into the slot.
The traverse mechanism shown in FIGS. 3A-D also has substantial free length, between the edge of the slot where the strand exits the slot 54 and the strand's contact point with the package surface. As noted above, this traverse mechanism is also useful only with packages wound with low tension and therefore susceptible to compression at the ends to produced a cylindrical package.
The shape of the packages produced by, and the engagement with the packages by, the traverse mechanisms described above are illustrated in FIGS. 4A, 4B. In both mechanisms, the traverse mechanism remains in continuous contact with the package during operation (the roller bail in FIG. 4A and the strand guide in FIG. 4B.
FIG. 4A shows the relationship between the split rollers 19 of the winding mechanism shown in FIGS. 1 and 2 and a package 20. A split roller 19 is positioned at each end portion 22 of the package 20. As previously discussed, some packages tend to develop a "dog-boned" shape as they are wound, particularly those packages with high winding speed and tensions and therefore high, uniform density. The radial force applied by the split rollers 19 against the ends of the package 20 slightly flattens the end portions 22. FIG. 4B shows the relationship between the strand guide of FIGS. 3A-3D and a package 20 that is being wound. The strand guide 50 remains in continuous contact with the outer surface of the package 20 as it reciprocates in the directions of the arrows as shown. As discussed above, strand guide 50 flattens any "dog-boning" that develops on the package 20. The result is a package with a uniform outer surface diameter as shown in FIG. 4B.